This invention concerns manufacturing of molded plastic glazing panels, particularly curved glazing panels used in automotive vehicles.
The use of molded plastic glazing panels for the windows of automotive vehicles offers many advantages, such as reduced weight, superior resistance to fracture and/or dislodgment in the case of accidents, and greater freedom in vehicle styling due to the ease of forming glazing panels in any desired shape.
These advantages have not heretofore been realized on a large scale due to the difficulty in matching the optical clarity and scratch resistance of conventional glass panels. Such plastic panels must be resistant to obscuration due to UV radiation exposure, and must also block UV transmission to prevent deterioration of interior trim surfaces and fabric materials by UV radiation.
Polycarbonate has been widely proposed for this application, and the technology for hard coating this plastic has been developed which allows for the manufacture of UV and scratch resistant plastic glazing panels. This technology involves coating the panels, as by dipping the panels in tanks of liquid coating material and subsequent curing of the coating in an oven. Other coating processing steps have been developed as well for this application, such as a plasma coating.
In the automotive industry, any defect in a glazing panel which creates a visible optical flaw during the handling and processing would result in rejection of the part. Accordingly, handling and processing must be carried out in such a way as to minimize creating optical flaws.
The manufacture of automotive components is done on a vast scale in a very competitive environment, and thus, the processing of glazing panels must be carried out highly efficiently while still producing quality parts. There is a high probability of producing defective parts while handling the panels during dipping into a tank of liquid coating, as drips or the running of the liquid coating material onto the glazing may result in a visible flaw.
At the same time, the distinct curved shape of the glazing panels makes compact racking of the panels difficult. Any bumping of the panels as they are racked may also create scratches or other surface defects necessitating rejection of the part.
Accordingly, it is an object of the present invention to provide a method for handling of molded plastic glazing panels during processing steps which minimizes the incidence of optical flaws, yet allows large numbers of the panels to be efficiently handled during processing, and compactly stacked together in a vertical array.